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N2 in naphtha reformer feed

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Milutin

Milutin

Chemical
Jul 7, 2006
152
Hi all,

Few weeks ago we noticed higher nitrogen content in straight run naphtha, which is feed for HDS unit before entering reformer unit.
Usual nitrogen content in SR naphtha is 1.5 to 1.0wppm, and below 1wppm in hydrotreated naphtha.
Now we have nitrogen content about 3.5 to 4.5wppm in SR naphtaha and 2.5 to 3.5wppm in hydrotreated naphtha.

To eliminate possibility that crude unit dosing chemicals cause increased nitrogen content in SR naphtha we cut crude oil on laboratory to 60-180degC cut, and get result 4.5wppm for nitrogen content, what eliminate crude unit as source of increased nitrogen.

Also analyzing light naphtha , FBP below 70degC, we find result 6.8wppm, what surprise me.

We got similar result for two different types of crude oil, from different suppliers.

As natural nitrogen compounds present in naphtha (pyridine , piperidine pyrrole etc.)have boiling point above 100degC, it seems that nitrogen is "added" in refinery, possibly slop mixing, but we didn't noticed increased sulfur or olefines content in SR naphtha.

What can cause such increase of nitrogen in SR naphtha?

Regards,

Milutin
 
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Is contamination with naphtha from thermal processes, such as VB, coker, or even FCC, possible ?
 
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Hi 25362,

It is possible contamination with FCC naphtha, but if that happens I would expect increased sulfur content and olefin content, values for this compounds doesn't changed.

What would happens if DEA is present in naphtha, would it be easily destroyed in HDS reactor?

 
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Are you referring to the DEA-treated recycle gas ?

Typical naphtha HDS units are based on Co/Mo catalysts and operate at relatively low pressures. The HDN is partial when compared with HDS.

To remove organic nitrogen compounds to these required low levels may need much higher pressures and probably a Ni/W type of catalyst.
 
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Yes, DEA from gas scrubbing, we don have it in our naphtha HDS unit, but maybe is crude oil contaminated with DEA.
Reason for suspecting to DEA is high nitrogen concentration in SR light naphtha from crude unit, as boiling point of DEA is 55.5degC.
Is there any laboratory method for detecting DEA in petroleum streams?

Regards,

Milutin

PS. I apologize to all, in thread subject should be "nitrogen" instead "N2"
 
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Besides chromatography I don't know of a reliable method.

I was thinking of two other "remote" possible sources of nitrogen:

[•] Stripped water from SWS into the desalters
[•] Amines or ammonia injection to toppers' overheads

Could you check of any changes in these operations during the last few weeks ?
 
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To ruled out possibility of contamination in crude unit I already take samples of crude oil from crude oil tanks and fractionate naphtha fraction 60-180degC in our laboratory. Results are 4.5wppm nitrogen in that sample it means already increased nitrogen content before crude unit.

I am planing to take samples of crude oil from pipeline in front of refinery, and in that way check possibility if contamination is occurred in refinery crude oil tanks.

Regards,

Milutin
 
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I've heard that there are crudes like the one from Wilmington (California) that are reported to contain up to 27 ppm N in the fraction 130-250[sup]o[/sup]C. Thus, some N would appear in the 80-180[sup]o[/sup]C cut. BTW, 3-methylpyridine boils at 144[sup]o[/sup]C and pyrrole at 130[sup]o[/sup]C.
 
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If the N is from the crude itself, you will definitely want to change out your Naptha HDS cat for a potent NiMo like Criterion DN200 or equivalent.
 
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Milutin
One "crude" source could be from H2S scavengers used in crude oil production. Did see an NH3 effect from such a scavenger in the Crude tower top condensate. This came "suddenly" on a known crude. Did seem that some of this material cracked (thermally) in the crude furnace (like sulphur and H2S formation) and gave higher than ususal Nh3 values in the water.
However we did not see any problems on the hydrotreated naphtha, however we did only measure the product and not the feed so we didn't knew were this scavenger ended up in the crude tower product.
RH
 
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